They replaced peas with another vegetable. Before I ditched kibble over a year ago, I had phased Zupreem (corn-free) out of my kibble mix because I didn't trust it. Zupreem is deceptive about their ingredients (ingredient splitting) and even if you email them they refuse to indicate how much of the kibble is plant-based. It's likely to be a lot, and is therefore less than ideal for ferrets. Some of the more reputable kibbles like Orijen and Epigen 90 (digestive support version) openly state how much of it is animal-based. Even Evo, which many people distrust since the brand has been sold several times, is 87% meat-based. Anything less than 100% animal leaves at least a little room for improvement.
I don't know if one is significantly better than the other, both have tons of veggies and they use different ingredients to get particular benefits, ie. grain free uses fish (possibly for Omega 3 fatty acids) while the corn free one uses flax seeds. I still think the corn free one is marketed to be higher quality than the grain free but I wouldn't suggest either.
Ferrets: Contessa, Frankenfurter, Butterscotch. Kitties: Watson, Oskar DIP Sinnead, Vincent, Boris, Zeus and Athena, Willow, Mr. Frodo, Indie, Lucrezia, Judge, Odin, Miss Emily, Suki, Cody, Aristotle. RIP Herne, Ligeia, and Mr. Stubbs